sd-ndisc: disable one more timer event source

Otherwise, even if we have already received RA, timeout callback will be
called. Currently, networkd mostly does nothing on timeout, hence should
not change any effective behavior.

Follow-up for e7cb80474d.

src/libsystemd-network/sd-ndisc.c

@@ -219,6 +219,7 @@ static int ndisc_handle_router(sd_ndisc *nd, ICMP6Packet *packet) {
                 return r;
 
         (void) event_source_disable(nd->timeout_event_source);
+        (void) event_source_disable(nd->timeout_no_ra);
 
         log_ndisc(nd, "Received Router Advertisement: flags %s preference %s lifetime %s",
                   rt->flags & ND_RA_FLAG_MANAGED ? "MANAGED" : rt->flags & ND_RA_FLAG_OTHER ? "OTHER" : "none",